Many microorganisms produce pili or firmbriae on their cell surface. The proteins vary in functon depending on the organism. In many cases these surface structures enable the bacterium to adhere to their host or organism they subsequently interact with. Thus these surface structures play a primary role in host-parasite interaction. The pili produced by Neisseria gonorrhoeae are no exception. These pili function in the attachment of the gonococci to the human host and therefore is a primary determinant of pathogenicity, a major factor in cell-cell interaction. The gene(s) encoding pilus synthesis is turned on and off at high frequency. The phenotypes (P+ and P-) can be determined easily by light microscopy. There are at least 50 pili serotypes. The heterogeneity lies at the carboxyterminal end; the amino terminal end for the pilus subunit is very similar if not identical. Very little is known about the genetic regulation of pili expression in N. gonorrhoeae. For these reasons, the pili of the gonococci represent an interesting system for studying the regulation of gene expression. We propose to study the basis for pilus expression in N. gonorrhoeae. Using techniques in genetics (mutagenesis and complementation), DNA biochemistry (recombinant cloning, DNA sequencing, Southern hybridization), protein chemistry (SDS PAGE, 2-dimensional gels, Western blotting) and immunology (immunoprecipitation) we hope to elucidate the mechanism underlying the heterogeneity of pilus type as well as the genetic and molecular mechanisms regulating the expression of pili synthesis by the gonococcus.